You can still make macaroni and cheese even without the use of milk but the milk helps to add flavor and makes the cheese more cheesy tasting.
I've made macaroni and cheese without milk before because I ran out of milk and it still tasted okay.
You can also use Almond Milk or Soy Milk if you cannot use regular milk due to allergies or don't have any other milk or just add some butter or chicken broth to the macaroni and cheese.